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aTC529 R47
Channel and Watershed Processes Research Unit
National Sedimentation Laboratory
Oxford, Mississippi
ACTUAL AND REFERENCE SEDIMENT YIELDS FOR THE JAMES
CREEK WATERSHED MISSISSIPPI
-
By Andrew Simon, Ronald L. Bingner, Eddy J. Langendoen, and Carlos V. Alonso
Research Report No. 31 August 12, 2002
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ACTUAL AND REFERENCE SEDIMENT YIELDS FOR THE
JAMES CREEK WATERSHED - MISSISSIPPI
Prepared by
Channel and Watershed Processes Research Unit
National Sedimentation Laboratory
Oxford, Mississippi
For
Mississippi Department ofEnvironmental Quality
August 12, 2002
ACTUAL AND REFERENCE SEDIMENT YIELDS FOR THE
JAMES CREEK WATERSHED - MISSISSIPPI
ARS Designated Representative and Project Manager:
Carlos V. Alonso
Technical Direction, Data Analysis, and Report Preparation by:
Andrew Simon, Ronald L. Bingner, and Eddy J. Langendoen
Mapping, GIS and Model Execution:
Robert Wells, Yongping Yuan, Vance G. Justice, and Igor Jaramillo
Field Operations and Database Management:
Mark Griffith and Vance Justice
Field Data Collection and Data Processing:
Mark Griffith Charlie Dawson, Brian Bell, Robert Wells, Nick Jokay, Anthony Lazell, Lauren
,
Farrugia, IgorJaramillo, Micah Fendiesen, Vance Justice, and Yongping Yuan
11
1 1
EXECUTIVE SUMMARY
At the request and support ofthe Mississippi Department ofEnvironmental Quality
(MDEQ), the Channel and Watershed Processes Research Unit, National Sedimentation
Laboratory embarked on a 90-day study ofsediment loadings in James Creek, Monroe County,
Mississippi. The principal objective ofthe study was to determine “actual” sediment-transport
MDEQ
rates and rates for similar, but stable orunimpaired (“reference”) streams by which could
develop water-quality targets for sediment. Without historical sediment-transport data forJames
Creek a combination ofmethods were used including empirical analysis ofhistoric data from
other sites, field reconnaissance and detailed data collection and surveying, and numerical
modeling ofuplands and channels.
“Reference” suspended-sediment transport rates were obtained from stable streams with
historical flow and sediment-transport data in the Southeastern Plains Ecoregion. Using the
discharge that occurs, on average every 1.5 years (Q1.5) as the “effective discharge” and a flow
rate that represents long-tenn sediment-transport conditions, an initial “general reference” of
0.3 T/d/km was obtained. This value, however, is skewed towards streams with sand beds and
does not accurately reflect conditions along James Creek. A refined “reference” condition was
developed for stable silt/clay-bed streams in the Southeastern Plains resulting in a “reference”
suspended-sediment yield of3.23 T/d/km at the Q15. Although silt/clay bed substrates dominate
James Creek, some reaches’ substrate are largely sands and/or gravels. A weighted-reference
condition based on the percentage ofthe drainage area encompassed by the various bed-material
types results in a reference yield at the Q1.5 of2.22 T/d/km . This is converted to a “reference”
suspended-sediment load at the watershed outlet of249 T/d. Similarly, an equivalent weighted-
reference suspended-sediment concentration of 160 mg/1 was obtained.
“Actual” sediment-transport rates were obtained by three mechanisms: simulations offlow and
sediment transport using the AnnAGNPS watershed model and the CONCEPTS channel-
evolution model; and direct comparisons ofmeasured cross sections from 1967 and 2002.
AnnAGNPS simulations were conducted using actual precipitation data from Aberdeen,
Mississippi as well as using generated precipitation data. AnnAGNPS was used in combination
with CONCEPTS to take advantage ofthe best features ofeach ofthese models, AnnAGNPS for
uplands and CONCEPTS for the main-stem channel. The resulting simulated flows were
compared to peak flows recorded by the USGS at the Highway 25 bridge and showed close
agreement. Sediment-transport rates are provided for the watershed outlet, at Darracott Road,
and the Highway 25 bridge over the period 1967 - 2002.
Average sediment loads at the mouth ofJames Creek over the 35-year period are about 250,000
T/y with about 89% ofthis material emanating from James Creek and its tributaries with only 1
% derived from upland sources. Ofthis 89% eroded from the channel boundaries, about 88%
comes from the channel banks. This loading value, however, is somewhat misleading in that
severe channel erosion occurred between 1967-1968 following channel clearing and snagging
operations over the lower 17 km ofJames Creek. Since this time, sediment loads have attenuated
and the contributions from channels and uplands over the period 1970-2002 are 70% and 30%,
respectively.
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